Semiconductor workpieces are often implanted with dopant species to create a desired conductivity. For example, solar cells may be implanted with a dopant species to create an emitter region. This implant may be done using a variety of different mechanisms. The creation of an emitter region allows the formation of a p-n junction in the solar cell. As light strikes the solar cells, electrons are energized, creating electron-hole pairs. The minority carriers, which are created by the energy from incident light, are swept across the p-n junction in the solar cell. This creates a current, which can be used to power an external load.
In some embodiments, one surface of the workpiece is doped so that the entire, or substantially the entire surface has a first concentration of dopant. Portions of that surface are more heavily doped to create regions where metal contacts may be attached. In some embodiments, this configuration is used to create a selective emitter solar cell. In this configuration, the workpiece beneath the metal contacts is heavily doped to insure good contact resistance and to shield the metal contacts from minority carriers. The rest of the surface, which is lightly doped, minimizes Auger recombination of minority carriers.
Ion implantation may be used to create this selective emitter surface using a plurality of implants. Therefore, a method of ion implanting that efficiently creates a workpiece with a lightly doped surface with regions of higher doping would be beneficial.